1. Field of the Invention
The present invention relates to an intravascular obstruction removing wire and medical instrument for removing an obstruction, for example, an embolus in a blood vessel.
2. Description of the Related Art
Death cases and sequelae caused by strokes increase in recent years, and postapoplectic therapy needs to be established as soon as possible. As a typical postapoplectic treatment, a thrombolytic treatment using a thrombolytic agent has been developed to treat acute cerebral infarct, and has achieved a satisfactory treatment effect. With the thrombolytic agent, however, sometimes thrombolysis takes time. A thrombus which is reduced in size may be scattered to form another embolus portion. Some thrombus may not be dissolved by the thrombolytic agent. These inconveniences are acknowledged from the clinical experiences of doctors.
In the case of a cerebral infarct, if the blood flow can be resumed within three hours after the infarct is developed, not only the probability of saving the patient's life increases, but also sequelae can be reduced. This is verified in the U.S.A and Europe. Development of a medical instrument that can be inserted in a cerebral blood vessel and can directly remove a thrombus has accordingly been strongly sought for.
Conventionally, as an apparatus for removing a thrombus or obstruction in a blood vessel, for example, a Fogarty catheter of, e.g., U.S. Pat. No. 3,435,826 by Fogarty, an expandable thrombus removing balloon, a water-jet thrombus sucking apparatus, and an atheroma cutter of U.S. Pat. No. 4,842,579 have been made practicable and used. These apparatuses have a complicated structure and a large diameter, and are used alone or require a thick guide catheter. An apparatus that can be inserted in a microcatheter has not been made practicable.
For example, an ablation catheter with a wire basket is typically disclosed in Jpn. Pat. Appln. KOKAI Publication No. 5-137729 (EP 472,368). This catheter has an acute angled portion in part of its wire cage in order to ablate tissue from the inner wall of a blood vessel. The catheter also has a wire guide at its center to support the wire cage. The diameter of this catheter cannot essentially be reduced to be equal or smaller than that of the wire guide. In other words, the wire guide is indispensable for ablating the tissue by rotating the wire cage. Accordingly, the diameter of this catheter cannot be reduced to be equal or smaller than that of the wire guide.
Japanese Patent No. 2,620,881 (U.S. Pat. No. 4,890,611) discloses an endarterectomy apparatus with a wire loop. This apparatus is designed to shear arteriosclerotic deposits. With the structure of this apparatus, it is difficult to hold a thrombus that blocks up a blood vessel. More specifically, a central wire and helical loops cannot form a large holding space, but can merely provide a narrow space where the sheared tissue is to be held. Due to the presence of the central wire, a thrombus cannot be easily accommodated in the helical loops. Therefore, the tissue to be ablated can merely be sandwiched between the central wire and the helical loops.
Jpn. Pat. Appln. KOHYO Publication No. 8-509411 (WO95/31149) discloses a single-loop medical collecting instrument formed of a snare coil. This tool is used to rearrange or extract an obstruction by nipping it with an adjustable-diameter single loop. A medical collecting instrument of the type conventionally called a single-loop gooseneck snare has a simple structure, and its diameter can be reduced. With this instrument, a target obstruction is trapped in the single ring of a single wire, and is held by fastening the ring. Although this instrument is suitable for holding a thin, elongated rod-like obstruction, it is difficult for this instrument to grip an obstruction such as a thrombus which is slippery. In other words, when the target obstruction is a thrombus, to hold it is equivalent to fixing an egg by applying the loop of one wire around it. Although this instrument can be theoretically used, it is difficult to hold an obstruction with the instrument except for a highly-skilled operator.
Jpn. Pat. Appln. KOKAI Publication No. 2000-126303 discloses a multi-functional wire for blood vessel treatment which can be inserted in a microcatheter. This multi-functional wire is of the type conventionally called a basket forceps. A basket which can be contracted and expanded by a wire is formed at the distal end of the wire. This multi-functional wire is obtained by refining a conventional basket forceps by making it much thinner. This multi-functional wire integrally has an expanding action part which is radially dispersed or expanded and gathered or adhered at a convergence point. Hence, in this multi-function wire, the constituent fine lines lose the degree of freedom, and a thrombus cannot be accommodated in the basket easily.
Jpn. Pat. Appln. KOHYO Publication No. 7-504595 (WO94/00178) discloses an instrument in which an expandable metal net is attached to the distal end of a catheter. In this instrument, as the metal net is attached to the distal end of the catheter, it is difficult to reduce the outer diameter of the instrument to be smaller than that of the catheter.
Jpn. Pat. Appln. KOKAI Publication No. 7-171156 (U.S. Pat. No. 5,370,653) proposes an apparatus which removes a thrombus by enmeshing it with a wire brush. Although this apparatus is useful for enmeshing a glue-like soft obstruent such as fibrin, it is difficult for this apparatus to remove a hard thrombus or the like that blocks up a blood vessel. Therefore, when the obstruction is a soft obstruent such as fibrin, it can be removed better by dissolving it with a dissolving agent such as streptokinase or urokinase rather than by removing it by force with this apparatus.
As a technique for removing a hard thrombus that blocks up a blood vessel, a wire disclosed in U.S. Pat. No. 5,895,398 is known. This wire has, at its distal end, a screw structure that can be inserted in a microcatheter. According to this apparatus, the screw portion is screwed into a thrombus like a cork screw. The thrombus is collected just like uncorking a wine bottle. This apparatus is not reliable because, when the screw is screwed into the thrombus, the thrombus may slip off and escape easily. Moreover, the screw may undesirably damage the blood vessel by piercing it.
Jpn. Pat. Appln. KOKOKU Publication No. 4-47574 (U.S. Pat. No. 4,590,938) proposes a wire basket-type medical retriever having a coaxial central sheath. This retriever is characterized in that a large number of wires form a bulb-shaped obstruction trapping space. This apparatus must have a shaft sheath at its center. Due to the presence of the shaft sheath, this apparatus cannot provide a large trapping space.